linux-kernel - Re: [PATCH] Add RWF_NOSIGNAL flag for pwritev2

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Message-ID: <6c85f96a-f012-48e9-a2fa-f1c7650d8533@kernel.dk>
Date: Fri, 29 Aug 2025 05:03:55 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Lauri Vasama <git@...ama.org>, Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemb@...gle.com>, "David S. Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>
Cc: Jan Kara <jack@...e.cz>, Simon Horman <horms@...nel.org>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH] Add RWF_NOSIGNAL flag for pwritev2

On 8/27/25 7:39 AM, Lauri Vasama wrote:
> For a user mode library to avoid generating SIGPIPE signals (e.g.
> because this behaviour is not portable across operating systems) is
> cumbersome. It is generally bad form to change the process-wide signal
> mask in a library, so a local solution is needed instead.
> 
> For I/O performed directly using system calls (synchronous or readiness
> based asynchronous) this currently involves applying a thread-specific
> signal mask before the operation and reverting it afterwards. This can be
> avoided when it is known that the file descriptor refers to neither a
> pipe nor a socket, but a conservative implementation must always apply
> the mask. This incurs the cost of two additional system calls. In the
> case of sockets, the existing MSG_NOSIGNAL flag can be used with send.
> 
> For asynchronous I/O performed using io_uring, currently the only option
> (apart from MSG_NOSIGNAL for sockets), is to mask SIGPIPE entirely in the
> call to io_uring_enter. Thankfully io_uring_enter takes a signal mask, so
> only a single syscall is needed. However, copying the signal mask on
> every call incurs a non-zero performance penalty. Furthermore, this mask
> applies to all completions, meaning that if the non-signaling behaviour
> is desired only for some subset of operations, the desired signals must
> be raised manually from user-mode depending on the completed operation.
> 
> Add RWF_NOSIGNAL flag for pwritev2. This flag prevents the SIGPIPE signal
> from being raised when writing on disconnected pipes or sockets. The flag
> is handled directly by the pipe filesystem and converted to the existing
> MSG_NOSIGNAL flag for sockets.

LGTM, only curiosity is why this hasn't been added before.

Reviewed-by: Jens Axboe <axboe@...nel.dk>

-- 
Jens Axboe